Message Passing Without Temporal Direction: Constraint Semantics and the FITO Category Mistake

TL;DR

This paper challenges the traditional view of message passing in distributed systems by arguing it is based on a category mistake, and proposes a symmetric, constraint-based framework that does not rely on temporal causality.

Contribution

It formalizes the misconception of temporal causality in message passing, introduces a constraint semantics framework, and proves an equivalence between message passing and constraint satisfaction problems.

Findings

Message passing can be represented as constraint satisfaction problems.

Temporal causality assumptions are representational artifacts, not ontological primitives.

The framework connects message passing to concepts like Lamport clocks and relativity.

Abstract

Message passing is widely assumed to be a fundamental primitive of distributed systems. This paper argues that conventional message systems embed a category mistake: they misinterpret logical dependency relations as temporal propagation processes. This error arises from an implicit Forward-In-Time-Only (FITO) assumption, which treats causality as intrinsically directed along a temporal axis. We formalize FITO as the imposition of a partial order over events and show that clocks, scheduling, and message propagation are representational artifacts rather than ontological primitives. We then reformulate interaction in terms of symmetric constraint relations, identify the minimal substrate of interaction independent of temporal direction, and prove an equivalence theorem: under mild assumptions, a broad class of message-passing executions can be represented as constraint satisfaction problems, and conversely, constraint satisfaction instances can be realized as message-passing protocols. We connect the result to Lamport clocks, Hewitt actors, Pratt pomsets, category theory, relativity, and indefinite causal order, and interpret engineering consequences for reflective and reversible link architectures such as Open Atomic Ethernet.